Improved controllable inductance apparatus



July 16, 1957 G. H. DEWITZ I 2,799,822

IMPROVED CONTROLLABLEZ INDUCTANCE APPARATUS Filed July 22, 1952 FIG. 2.

SOURCE OF CONTROLLED CQNTROL CIRCUI T5 p vr INVENTOR GER/ HEB H. QEW/TZ4:475, fiowlr ir/$14. v ATTORNEW IMPROVED CONTROLLABLE INDUCTANCEAPPARATUS Gerhard H. Dewitz, Westport, Conn, assignor to C. G. S.Laboratories, lnc., Stamford, Conn., a corporation of ConnecticutApplication July 22, 1952, Serial No. 300,196

8 Claims. (Cl. 32389) This invention is in the field of high frequencysaturable core magnetic apparatus in which the inductance of a signalwinding is controlled electrically by varying the magnitude of a currentsent through a control windmg.

In such controllable inductors, sometimes called saturable reactors, thecontrol current acts to regulate the degree of the magnetic saturationof the core and thereby to control the effective inductance of one ormore other signal windings wound on the same core. Such a saturable coredevice using ferromagnetic ceramic core material is described in mycopending application, Serial No. 213,548, filed March 2, 1951. Thatdevice is provided with a ring core having a rectangular slot or openingthrough the rim. The controlled winding, called the signal winding, iswound in two portions through this opening and produces flux lines whichclose around the opening.

According to the present invention the cores are provided with graduallychanging or varying cross sectional area in the region of thi signalwinding so as to provide control of the degree of saturation of variousportions of the core and to regulate the rate at which this saturationoccurs. By this means substantially linear control characteristics canbe obtained over any desired portion of the operating range and otherspecial characteristics are readily obtained, which have particularapplication in computing devices.

The present invention will be described as embodied in controllableinductors having ferromagnetic ceramic ring cores. Several embodimentsof the invention have been illustrated and described in order to setforth fully the principles of the invention and so that it can beapplied readily in each condition of use and to make apparent thevarious aspects, advantages and objects of the invention.

Figure 1 of the accompanying drawings shows a controllable inductorembodying the present invention;

Figure 2 is a plan view ofthe core of the inductor of Figure 1;

Figure 3 is an enlarged partial elevational view of the core shown inFigure 2.

Other arrangements of the invention are illustrated in Figures 4 to inwhich the windings have been omitted from the cores in order toillustrate more clearly the differences therebetween.

Figures 4 and 5, respectively, are perspective and front views ofinductors in which the cross sectional area of the entire coreprogressively changes throughout its circumference;

Figures 6 and 7 are perspective and front views, respectively, of a ringcore, generally indicated at 14 and having an oval hole therein;

Figure 8 is a perspective view of an inductor having a circular hole inthe core through which the signal winding extends;

Figure 9 shows a similar core having a diamond-shaped opening; and

Figure 10 shows a core having a rectangular slot in which the radialthickness of the core decreases gradually from each end of the slot to aminimum at the center of the slot.

The inductor, generally indicated at 2 in Figure 1, includes a ring core4 of ferromagnetic ceramic material such as is disclosed by Snoeck in U.S. Patents 2,452,529, 2,452,530 and 2,452,531. Other ferromagneticsaturable materials such as Mu-metal, Permalloy, soft iron and the likemay be used. However, the ceramic materials offer marked advantagesbecause of their higher Qs, their high permeability and wide operatingrange, etc. A slot 6 is provided in the core for a purpose to be madeclear presently.

The ring core 2 has a first portion of substantially uniform crosssectional area, but between the broken lines 8 and 10 (Figure 3) thecross sectional area of the core gradually decreases and reaches aminimum substantially at the center of the slot 6. This reduction incross section is obtained by arcuate recesses, generally indicated at 12and 14, on the top and bottom of the core.

The core 2 carries around its uniform portion a control winding 16,usually having a relatively large number of turns. This winding 16 isconnected to a suitable source of control current indicateddiagrammatically at 18, and the magnetic saturation of the entire coreis controlled by the current flowing through this winding in a mannerwell known in the art of saturable core magnetic apparatus. This controlcurrent produces a flux flowing in a closed loop through the core 10,for instance, this saturating flux may flow in the direction representedby the arrows 20 in Figure 2.

In order to cancel out any undesired magnetic coupling between thecontrol winding 16 and the signal winding 22, the signal winding 22 isformed in two equal sections 22-1 and 222. These winding portions arewound through the slot 6 and around opposite rim portions of the core 4.The two sections 22-1 and 22-2 are connected in series in such mannerthat flux lines formed by current flowing through the winding 22 closearound the slot 6.

Thus, the slot 6 divides the core 4 into two spaced branches and one ofthe sections of signal winding 22 is wound around each of thesebranches. The magnetic flux created by the signal winding 22 extends inone or the other direction in a closed loop around the slot 6. All ofthe saturating flux 20 in the core 4 produced by the control winding 16extends through the restricted cross sectional areas of the two spacedbranches of the core adjacent the slot 6.

As the control current through the control winding 16 varies, themagnetic saturation of the core material adjacent the slot 6 varies andthus varies the incremental permeability (or inductance) of the signalwinding 22, and this inductance acts to regulate the controlledcircuits, diagrammatically shown at 26. If the cross sectional area ofthe core 4 were constant throughout the flux path associated with thewinding 22, all of the core material in this path would be saturated tothe same extent at any given instant of time. In the constructions usedheretofore the two core branches on either side of the slot operated atall times on corresponding portions of their saturation curves andreached saturation at the same time throughout their entire lengths.With the arrangement shown in Figures 1, 2 and 3, the core portion withthe smallest cross-sectional area saturates first and then succeedingportions of the core with larger cross sectional areas are saturated asthe control current increases.

The effect of the saturation can be explained best by considering theaction of individual portions of the core 4 as the control currentincreases from zero to a maximum value. The divided signal winding 22 isassumed to be carrying an alternating signal current, at least severaltimes the maximum frequency of the highest frequency components of thecontrol current. The control current may be either alternating orunidirectional as described in the afore-mentioned copendingapplication.

When the control current is zero, there is relatively low reluctance int.e magnetic path around the slot 6, and consequently the signal windinghas maximum effective inductance.

As the control current is increased, the saturation of the core brancheson each side of the" slot 6 increases thus causing an increasedreluctance to the flow of the signal flux around the slot 6 and henceprogressively reducing the inductance in the signal current circuit 26.As the control current is still further increased, the portions of thecore 4 having the least cross-sectional area, indicated at 28 in Figure3, are the first to reach saturation, and the magnetic permeability atthese points is reduced substantially to unity or that of air.Initially, the region of this full saturation is confined to arelatively small length of the core. At increasing distances in eitherdirection from the saturated portions of the core, the cross-sectionalarea of the core increases and the extent of magnetic saturationaccordingly decreases. The saturated portions of the core form virtualor imaginary air gaps whose widths increase as the control current isincreased.

Because of the gradual change in cross-sectional area of the coreadjacent the slot 6, and the consequent spread of the operationthroughout the saturation curve, an effect substantially difierent innature is produced from that which is attained With uniform coredimensions. Thus, if the core has uniform outer dimensions andarectangular slot, all of the core material on each side of the slotoperates at any given instant at the same point on the saturation curveof the core material and the entire length of this material reachessaturation at'the same instant, at which time substantially all controlover the inductance of the signal winding is lost. Thus, with such aconstruction no virtual air gap is formed during the time in which anysubstantial control over the inductance of the signal winding is beingexercised.

In addition, this gradual transition in the magnetic saturation of thecore branches adjacent the slot 6 along their lengths appears to have abeneficial effect on the hysteresis of the controlled inductance so thatit more nearly follows the same path during increase and decrease of thecontrol flux 20. One possible explanation may be as follows: During thetime the control current is above a predetermined minimum, the magneticconditions within the branches adjacent the slot 6 range through thefull gamut from substantially full saturation to slight saturation. Asthe control flux varies above this minimum, there is less efiectivechange in this range of magnetic conditions within the branches, for anyfurther increase in the control flux increases the effective lengths ofthe virtual air gaps and substantially the same degree of saturationexists at points in the core which are at a slightly increased distancefrom the centers 28 of the effective air gaps.

The form of the arcuate recesses 10 and 12 and the size and shape of theslot 6 control the relationship between the minimum control currentnecessary to cause the initial formation of the effective air gaps andthe rate at which these gaps become wider as a function of the controlcurrent. By suitably shaping the core portions or branches havingreduced crosssectional areas on either side of the slot 6, theinductance of the signal winding 22 can be made a wide variety ofdesired functions of the control current, and linear operation overrelatively wide ranges can be attained readily.

The arrangement described above has particular advantage when the coreis formed of ferromagnetic ceramic material. This is because the lossesin the core material remain low or actually decrease with increasedmagnetic saturation, and the reduced core portions can therefore beoperated efliciently even though their average magnetic saturation isrelatively high.

Thus, by forming the core 4 as described in order to modify the degreeof saturation occurring in various portions hereof associated with thesignal winding 22, I not only improve the control action characteristicsby regulating the relationship between the inductance of the signalwinding and apparently reducing the hysteresis effect in the controlledinductance, but also in some instances may actually increase theefficiency by reducing the average losses.

In Figure 4 is shown another embodiment of the present invention, inwhich the core 30 is tapered or provided with a changing cross-sectionalarea throughout its total length so that the portion 32 adapted toreceive a .control winding similar to the winding 16 shown in Figure 1,has a relatively large cross-sectional area. An elongated slot 34 isproivded in the signal winding portion of the core 36, which has arelatively small crosssectional area. The signal winding is woundthrough this slot 34 around the two rim portions or core branches 36formed thereby in a manner similar to the winding 22 shown in Figure 1so that a current flowing therethrough produces a flux which closes in aloop around the slot 34.

The operation of this core 30 is different from that of the core 4. Forexample, as the bias or control flux flowing around the ring core 30 isincreased, saturation of the branches 36 is more nearly uniform than thecorresponding saturation of the branches of the core 4 during similaroperation, because of the more gradual change in cross section thereof.

As the control flux is further increased the branches 36 begin to reachfull saturation and virtual air gaps are produced in the centralportions thereof. Because of the gradual rate of change of the crosssectional area of the branches 36, the effective air gaps producedtherein are varied in width at a proportionately faster rate for anypredetermined change in control flux. Thus, the form of the core 30provides an increased sensitivity of the controlled inductance tochanges in the control flux 38. The same maximum control flux produces amuch wider effective virtual air gap and consequently .a lower value ofcontrolledinductance than in the case of the core 4.

In Figures 6 and 7 are shown a ring core 40 with an ellipticaltransverse opening 42 formed therein. As seen in Figure 7, .the opening42 divides the core 40 into two branches. 44 having varying crosssectional area and adapted to receive the signal winding. Theoperational characteristics of the core 40 are somewhat similar to thecore 4. However, while the variation of the cross sectional area of rimportions 44 is gradual .at regions near the center thereof, the rate ofvariation of this cross section becomes increasingly greater toward theextreme ends of the hole 42. I have found that the core form shown inFigures 6 and 7 produces an inductance in the signal winding which issubstantially a linear function of the magnitude of the control currentthroughout a wide range of operation.

Figure 8 shows a ring core 46 with a transverse circular opening 48therein forming a pair of rim portions 50 adapted to receive a controlwinding similar to the winding 22 shown in Figure l. The operation of'the core 46 is somewhat similar to that of core 40, but because of therelative short length of the branches S0 and the greater average rate ofchange in the cross sectional area thereof, a smaller change in controlcurrent produces a greater proportionate change in controlledinductance. Moreover, the average reluctance of the magnetic controlpath around the ring 46 is reduced so that a relatively smaller minimumcontrol current produces full saturation of the central portions of thebranches 50. Thus, the effective virtual air gaps are produced at aminimum value of control current, resulting in the advantageous controlcharacteristics of this effect, as discussed in connection with Figure3. The shape of the inductance control curve is regulated even atrelatively low values of the control current.

In Figure 9 is shown a ring core 52 having a diamondshaped opening 54therein forming a pair of core branches 56 adapted to receive a signalwinding. The larger dimension of the hole 54 is parallel with thebranches 56. These branches or rim portions 56 have a uniformly changingcross sectional area.

In Figure 10, the ring core 58 hasa slot 60 therein forming the twobranch magnetic paths 62. A curved recess 64- in the outside surface ofthe core reduces the cross sectional area of the central segments of thebranches 62. An advantage of this form of the core 58 is that the pathlength for the control flux which flows in the core 58 is a minimum andhence offers a low reluctance to the control flux. Also, this minimumreluctance is obtained in spite of the presence of the large centralopening 68 which allows the control winding to have many turns so that asmall control current is required for operation.

It is to be understood that the principles set forth above in connectionwith single ring cores apply equally well to multiple ring corestructures using two or more cores.

From the above description it will be apparent that the saturable coremagnetic units embodying the present invention are well adapted toattain the ends and objects set forth herein and that the variousembodiments of the invention shown herein can be modified so as toproduce operating characteristics best suited to the needs of eachparticualr use.

I claim:

l. A controllable inductance including a closed core of ferromagneticmaterial having a first closed flux path therein and having a transverseopening therein extending transversely across said first flux path andbeing elongated in the direction of said first flux path and formingfirst and second parallel magnetic branches extending along oppositesides of said elongated opening, a control winding around a portion ofsaid core and around a portion of said first flux path for regulatingthe degree of magnetic saturation of the parallel magnetic branchesadjacent said opening, and a signal winding having first and secondportions connected in series and both being wound through said openingand respectively around said parallel magnetic branches of said core andleads from the ends thereof connectible to external circuits, the totalcross-sectional area of said core decreasing gradually in the vicinityof said elongated opening and having its minimum crosssectional areaadjacent the central portions of said parallel magnetic branches, saidparallel magnetic branches having a larger cross sectional area at theirends adjacent opposite ends of said transverse opening than in theircentral portions, whereby the degree of magnetic saturation of saidbranches progresses from a minimum near the ends thereof to a maximumnear their central portions.

2. Improved controllable inductance apparatus including a closedferromagnetic ring core having a transverse opening therein defining apair of adjacent branch portions passing on opposite sides of saidopening, said opening being elongated in the direction of thecircumference of said closed core and extending radially through the rimof said ring core, a control winding carried by said core for regulatingthe degree of magnetic saturation of said branch portions, and a signalwinding divided into two equal portions connected in series, each one ofsaid signal winding portions being wound around one of said adjacentbranch portions and both said signal winding portions extending throughsaid elongated opening, said branch portions completing a closedmagnetic path around said elongated opening, the reluctance of saidclosed path being a function of the saturation of said branch portions,said branch portions having a smoothly decreasing crosssectional areafrom their ends with maximum cross sectional area being at either end ofsaid elongated opening and with minimum area in their central portions.

3. Improved controllable inductance apparatus including a closedferromagnetic core having a first fiux path therein and an ellipticalopening therein with its elongated dimension parallel to the directionof said first flux path and defining a pair of branch portions passingalong opposite sides of said elliptical opening, a first winding carriedby said core and spaced from said opening, said first winding encirclingsaid first flux path, said elliptical opening causing said branchportions to have a progressively decreasing cross-sectional area fromtheir ends toward their central portions, the minimum cross-sectionalarea of said branch portions being near the center portion of saidelliptical opening and a second winding having two equal windingportions connected in series with each other and each extending throughsaid opening and around one of said core branches and being connectibleto external circuits.

4. A ferromagnetic ceramic ring core defining a large central openingand having a curved body portion curved around said large centralopening and a pair of spaced branch portions between the ends of saidbody portion, said branch portions passing along opposite sides of anddefining an elongated transverse opening extending through said ringcore and connecting with said central opening, said opening beingelongated in a direction parallel with said branch portions, acontrolwinding on said body portion and arranged to carry a controlcurrent for regulating the degree of magnetic saturation of said branchportions, said branch portions completing a closed magnetic path aroundsaid transverse opening whose reluctance is controlled by the currentflowing in said control winding, a central portion in each of saidbranch portions, said branch portions having a progressively reducedcross-sectional area from the ends of said body portion toward saidcentral portions, whereby the relative magnetic saturation of thecentral portions of said branches caused by flux flowing through saidbody portion exceeds the saturation of the ends of said branches, and asignal winding divided into two equal parts connected in series and bothextending through said elongated opening, one of said equal windingparts being wound around one of said branch portions and the other beingwound around the other of said branch portions, said signal windinghaving terminals connectible to external circuits.

5. A controllable inductance comprising magnetically permeable coreapparatus substantially completely defining a closed magnetic flux pathand including magnetically permeable core means defining an elongatedopening which is elongated in a direction substantially parallel withsaid magnetic flux path and which converges toward pointed ends, a pairof generally parallel branch portions extending along opposite sides ofsaid elongated opening, said opening being elongated in a directionsubstantially parallel with the longitudinal axes of said branchportions, said branch portions having central parts of smaller crosssectional area than their ends, the ends of each branch portion havingprogressively larger cross sectional area in a direction away from theircentral parts, the central region of said opening being wider than saidpointed ends, a signal winding having first and second portionsconnected in series and wound through said opening and respectivelyaround said opposite branch portions with leads therefrom connectible toexternal circuits, and magnetic control means for controlling themagnetic saturation of said parallel branches.

6. A controllable inductance as claimed in claim 5 and wherein thepointed ends of said elongated opening are triangular in appearance.

7. A controllable inductance comprising magnetically permeable coreapparatus substantially completely defining a closed magnetic flux pathand including magnetically permeable core means having a transverseopening therein extending transverse to said flux path and elongated inthe direction of said flux path and a pair of parallel branch portionspassing on opposite sides of said opening and forming, said openingbeing elongated in the direction of the longitudinal axes of said branchportions, said branch portions completing a magnetic path around saidtransverse opening whose reluctance is controlled by the magneticsaturation of said branch portions, said branch portions having reducedcross sectional areas near their central regions and tapering towardlarger cross sectional areas at each end, a signal winding having firstand second portions connected in series and wound through said elongatedopening and respectively around said branch portions and leads therefromconnectible to external circuits, and magnetic control means forcontrolling the magnetic saturation of said parallel branches.

8. A controllable inductance comprising magnetically permeable coreapparatus substantially completely defining a closed flux path andincluding core means defining a transverse opening therein extendingtransverse to said flux path and being elongated in the direction ofsaid flux path and having a pair of parallel branch portions ofmagnetically permeable material passing along opposite sides of saidelongated opening an bo h ng lud a flux path, said branch portionshaving a smaller cross sectional area near their central regions than ateither end, theends of each branch portion being tapered to increase incrosspsectional area toward the ends, the outer surfaces of each of saidbranch portions having recesses therein with the deepest areas of therecesses lying adjacent to the central regions of said branches a signalwinding having first and second portions connected in series and woundthrough said opening and respectively around said opposite branchportions with leads therefrom connectible to external circuits, andmagnetic control means for controlling the magnetic saturation of saidparallel branches.

References Cited in the fileof this patent UNITED STATES PATENTS1,722,167 Wilson July 23, 1929 2,241,912 Kersten et a1. May 13, 19412,284,406 DEntremont May 26, 1942 2,332,879 Weis Oct. 26, 19.432,452,529 Snoek Oct. 26, 1948 2,755,446 Gabor July 17, I956

